Alpha olefins may be oligomerized to prepare synthetic lubricating oil base stocks which have desirable lubricating properties such as a low pour point and a high viscosity index (VI). However, many of these oligomerization products do not have the physical properties desired for certain applications, and they are often expensive to manufacture.
U.S. Pat. No. 4,827,064 discloses high viscosity polyalphaolefins that have high viscosity indices and low pour points. The high viscosity polyalphaolefins are characterized by a uniform molecular structure with low branch ratios. However, the polyalphaolefins are expensive to manufacture using conventional oligomerization processes.
U.S. Pat. No. 5,304,615 discloses a process for the polymerization of butenes using an ionic liquid as a catalyst, but the disclosure does not suggest a continuous process or the use of an ionic liquid composition derived from the combination of an alky-containing amine hydrohalide salt and a metal halide.
U.S. Pat. No. 5,731,101 discusses the possible use of low temperature ionic liquids as a catalyst for dimerization, oligomerization, and polymerization, but it does not specifically teach the oligomerization or polymerization of alpha olefins; and there is no suggestion of a continuous process using an ionic liquid to make polyalphaolefin products that are useful as lubricants or lubricant additives.
U.S. Pat. No. 5,824,832 is a continuation-in-part of U.S. Pat. No. 5,731,101 discussed above, and it focuses on the use of ionic liquids in the alkylation of aromatic molecules. The only exemplified reactions are those involving an aromatic compound, such as benzene and toluene. There is no suggestion of a continuous process using an ionic liquid to make a polyalphaolefin product.
EP 0791643 describes a process for oligomerizing alpha olefins, such as decene, using an ionic liquid catalyst to produce polyalphaolefins having a viscosity up to about 20 centistokes (cSt) at 100° C., but it does not teach the use of an ionic liquid composition derived from the combination of an alkyl-containing amine hydrohalide salt and a metal halide nor does it teach a continuous process. Additionally, the process taught in this application has not been shown to be suitable for making very high viscosity material, i.e., polyalphaolefins having a viscosity above 22 cSt at 100° C.
WO 95/21872 describes ternary compositions with ammonium halides are described in as being useful for olefinic oligomerization. Additional references discuss the use of imidazolium, pyridinium, or phosphonium as one component in the ionic liquid in addition to aluminum halide or gallium halide.
Considering the above discussed prior art, it is clear that there is a need for economical methods to produce high viscosity polyalphaolefins. Additionally, it is clear that there is a need for an economical process that utilizes the advantages of continuous processing for the manufacture of a polyalphaolefin product having certain desirable physical properties. Applicants have also found a continuous process for manufacturing polyalphaolefins having certain desirable properties.